CVE-2026-90948: GIMP ICO File Loader Buffer Overflow

CVE-2026-90948 Overview

CVE-2026-90948 is a heap-based buffer overflow in the GNU Image Manipulation Program (GIMP) ICO file loader. The flaw occurs when GIMP processes an ICO file containing an embedded Portable Network Graphics (PNG) image. An integer overflow during buffer size calculation results in an undersized heap allocation. When the decoder writes the decoded pixel data, it overflows the allocated buffer.

A remote attacker can craft a malicious ICO file and trigger the vulnerability when a user opens the file in GIMP. Successful exploitation can lead to arbitrary code execution in the context of the user or cause the application to crash. The weakness is classified as an out-of-bounds write [CWE-787].

Critical Impact
Opening a malicious ICO file in GIMP can lead to arbitrary code execution with the privileges of the current user.

Affected Products

GNU Image Manipulation Program (GIMP) — ICO file loader component
Red Hat distributions shipping the affected GIMP package (see Red Hat advisory)
Downstream Linux distributions packaging vulnerable GIMP versions

Discovery Timeline

2026-09-14 - CVE-2026-90948 published to the National Vulnerability Database
2026-09-16 - Last updated in NVD database

Technical Details for CVE-2026-90948

Vulnerability Analysis

The vulnerability resides in GIMP's ICO file plug-in, which parses Windows icon files. ICO containers can embed either a device-independent bitmap (DIB) or a full PNG image for each icon entry. When the loader encounters an embedded PNG, it decodes the image and allocates a heap buffer to hold the resulting pixel data.

The buffer size calculation multiplies attacker-controlled dimensions and per-pixel byte counts without adequate overflow checking. When these values are large enough, the multiplication wraps around and produces a value smaller than the actual pixel data. GIMP allocates the undersized buffer, then writes the decoded PNG pixels into it, corrupting adjacent heap memory.

Because the attacker controls the width, height, and channel configuration inside the malicious PNG, the size and content of the overflow can be shaped. This gives an attacker a path from file open to arbitrary code execution in the GIMP process.

Root Cause

The root cause is an integer overflow in the pixel buffer sizing arithmetic in the ICO loader. The multiplication of width, height, and bytes-per-pixel is performed in a fixed-width integer type without a prior overflow check. The truncated result feeds directly into the heap allocation, producing a buffer that is too small for the subsequent write loop.

Attack Vector

Exploitation requires a user to open a crafted ICO file in GIMP. Delivery vectors include email attachments, malicious downloads, shared project files, or icon assets bundled with other content. The Common Vulnerability Scoring System vector reflects local access with required user interaction, but the malicious file itself can originate from any remote source.

The vulnerability manifests entirely within the ICO loader's PNG-decode path. Refer to the GNOME GIMP Work Item #16742 and the Red Hat Bug Report #2533008 for upstream triage details.

Detection Methods for CVE-2026-90948

Indicators of Compromise

ICO files with abnormally large declared width, height, or bit-depth fields relative to their on-disk size
ICO files whose embedded PNG chunks decode to dimensions inconsistent with the ICO directory entry
GIMP process crashes, SIGSEGV, or heap corruption messages recorded shortly after opening an image file
Unexpected child processes spawned by the gimp binary following the opening of an image asset

Detection Strategies

Inspect ICO files at email and web gateways for malformed PNG payloads and inconsistent header dimensions
Monitor endpoint telemetry for GIMP process termination signals correlated with recent file-open events
Alert on GIMP spawning shells, scripting interpreters, or network utilities such as bash, python, nc, or curl
Correlate file write activity in user home directories with GIMP crash events to identify post-exploitation staging

Monitoring Recommendations

Enable core dump collection for GIMP on developer and creative workstations to preserve forensic evidence
Ingest process execution and file access telemetry into a centralized data lake for cross-host correlation
Track outbound network connections initiated by GIMP, which normally has no need for external communication
Baseline normal GIMP behavior per user role and alert on deviations such as new library loads or persistence writes

How to Mitigate CVE-2026-90948

Immediate Actions Required

Apply the patched GIMP package from your Linux distribution as soon as it is available
Instruct users to avoid opening ICO files from untrusted sources until patches are deployed
Block or quarantine ICO attachments at email gateways during the remediation window
Inventory workstations with GIMP installed and prioritize creative, design, and developer endpoints for patching

Patch Information

Refer to the Red Hat CVE-2026-90948 Advisory for the list of fixed package versions across Red Hat Enterprise Linux streams. Upstream tracking for the fix is available in the GNOME GIMP Work Item #16742. Users on other distributions should install the vendor-provided update once GIMP releases the corrected ICO loader.

Workarounds

Remove or disable the GIMP ICO plug-in in environments where ICO import is not required
Run GIMP inside a sandbox such as Flatpak, Firejail, or a container to constrain the impact of exploitation
Configure file managers not to auto-thumbnail ICO files with GIMP-based thumbnailers
Enforce least-privilege user accounts so that a compromised GIMP session cannot elevate to administrative access

bash

# Configuration example: remove the ICO plug-in on a Linux system
# Adjust the path to match your GIMP installation prefix and version
sudo rm -f /usr/lib/gimp/2.10/plug-ins/file-ico/file-ico

# Verify GIMP no longer registers the ICO loader
gimp --version
gimp -b '(car (gimp-version))' -b '(gimp-quit 0)'